In some wireless communication systems, transmission and reception functions are divided between an indoor unit (IDU) and an outdoor unit (ODU), typically located adjacent to the antenna. The IDU and ODU are connected by a link, which may be analog or digital. For example, U.S. Pat. No. 5,987,060, whose disclosure is incorporated herein by reference, describes a system and method for communication having a digital signal link connecting the IDU and ODU.
In some cases, the data rate of the communication system is variable. For example, U.S. Pat. No. 7,016,296, whose disclosure is incorporated herein by reference, describes methods and systems that enable subscribers to share a wireless channel by using different modulation schemes. The modulation scheme assigned to a subscriber is determined based on measurements of the quality of signals received from that subscriber. In one embodiment, the system is capable of transmitting data using one of a number of encoding and symbol constellation configurations.
As another example, U.S. Pat. No. 6,836,515, whose disclosure is incorporated herein by reference, describes a radio consisting of a multi-modulation modem, which modulates and demodulates signals using a plurality of modulations. The radio also comprises a frequency converter for converting the signals to a radio frequency and a transceiver unit including an antenna coupled to the frequency converter for transmitting the signals over a radio communications link.
As yet another example, PCT Publication WO 0076114 A1, which is incorporated herein by reference, describes a system for providing adjustable levels of information density in a communicated data stream in response to monitored communication link conditions.